PRH
Well-Known Member
I’m sure a phone call would get the answer.
Holley/Demon Carb stumble
- Thread starter Cudafever
- Start date
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I’m sure a phone call would get the answer.
I think, like me, sometimes you're reading fast and missing bits.
YR started those statements by saying he knows people (people he trusts as not BS) have positive results but, he hasn't.
Here's what I say at this point.
Solve this thing one step at a time.
If you are in the middle of race season, and you're committed (mentally) to the race dates, then make a decision as to what you will enjoy most.
IMO its really hard to race well when you're thinking about the car. And if you're making radical changes, there 's a darn good reason for that.
If you want to stick with the racing, then try small tweaks off of where you last raced.
If solving the issue is going to bring more satisfaction (or less frustration than trying to live with it while tweaking), then do that.
So far nothing has screamed the high position IFR is the next thing to change.
Maybe but i might have figured it out.
These are the spare part for the Proform 850 race carb.
https://www.summitracing.com/parts/pro-67201/replacementparts/brand/proform-parts
That's my main body and base plate...........so that must be the metering block to use?
Look and tell me what you think
These are the spare part for the Proform 850 race carb.
https://www.summitracing.com/parts/pro-67201/replacementparts/brand/proform-parts
That's my main body and base plate...........so that must be the metering block to use?
Look and tell me what you think
At this point I've almost completely lost track of what carbs you have and what metering blocks you've bought (seperate from carbs).
But I'm kindof with YR on this. Not sure what's special about 3310 blocks over a 4779, 4780, or 4710 or such.
If you want to experiement with a vacuum secondary carb, thats a different story. In that case try one of the 3310s.
Not sure what your plans are with the Might Demon, but it seems like that or one of the other shiny new items are candidates to be made more adjustable.
You'll need a tapp set with a bottoming tap. Maybe a couple different sizes depending on what you need to thread.
Someone from BLP said they have blocks with everything threaded including bottom IFR position so you have a choice. So if you don't want to tap, there's a probably as versitle of a block as can be bought.
If i was going to go out and buy a new carb it would be a race 750. BUT sence i seam to be building a carb one step at a time. i think the 850 metering block is my next step.
Still going to tinker with what i have and see what i can do. But really think i should get some Proform metering blocks coming.
As far as racing, if i was chasing points or taking winning a race, at the top of my priority. I would just put my 600 DP(List 6776) back on and live with a tenth slower car.
I'm not. I'm trying to make a consistent, faster carb/car.
Nobody is happy with the ET that they are making and i'm not any different
Appreciate your though on that metering block i posted up.
PRH
Well-Known Member
I have no idea if that’s correct or not.
I’d just make a call, or see if they’re listed on the Proform site as such.
I’d just make a call, or see if they’re listed on the Proform site as such.
I don't see anything obviously wrong with it.
Very similar to the one in the thread except maybe
Looks like it comes blank, so you'll need to drill set screws or buy the pre-drilled screws before using it.
Some have a bleed screws that are wide at top - like a jet, instead of bottoming out like a set screw.
Otherwise I think the restrictors are are mostly interchangable.
Very similar to the one in the thread except maybe
Looks like it comes blank, so you'll need to drill set screws or buy the pre-drilled screws before using it.
Some have a bleed screws that are wide at top - like a jet, instead of bottoming out like a set screw.
Otherwise I think the restrictors are are mostly interchangable.
And remind us all, with your old school 600 DP on it, there's no stumble or lean miss ?
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PRH
Well-Known Member
Honestly, at this point I’d just put the Demon back together like it was when it worked as good as it ever did, and reuse that as the baseline.
It has crossed my mind but it did the same thing that is happening now. (haven't found the problem) Before it all said and done it will be back together and a proven carb......the proven part is what i haven't found on either carb.
I sent a email out to proform on there metering block. waiting on a replay.
Time to wrap up my stitches on my thumb and see what i can figure out on the current combo.
PRH
Well-Known Member
I’m not going to go back and read thru the whole thread....... but I thought the new Proform body was running noticeably less MPH than the Demon body.
If that’s the case, and the new body is no more “bog free” than the Demon........ it just means you have another issue to deal with.
The bog........and a big main system calibration problem.
I say “big” because if it were close it wouldn’t be popping and losing multiple mph.
If that’s the case, and the new body is no more “bog free” than the Demon........ it just means you have another issue to deal with.
The bog........and a big main system calibration problem.
I say “big” because if it were close it wouldn’t be popping and losing multiple mph.
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not a 650 but a 600 DP
600 worked flawlessly. the only reason i put this carb on was because i when to a lower elevation track and I new the 600 was just to small.
So i rebuilt the demon carb and jetted it down a little and ran it down the 1/4 at 4400 foot elevation. it ran grate. so i dropped the jets down 2 more step for our local 6600 foot 1/8 mile track and it ran grate all last season. New converter, taller tires, new SS spring out back, and the problems started.
I haven't put the 600 back on for a race, but took it around the block. still works just fine.
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OK.
Corrected the 650 to 600 just as you replied. LOL.
I thought maybe we knew that the 600 will run as well with the tighter converter as it did with the looser converter.
But we do know the Demon ran well before. So that's good.
Tighter converter is definately less forgiving on the fueling and timing.
Corrected the 650 to 600 just as you replied. LOL.
I thought maybe we knew that the 600 will run as well with the tighter converter as it did with the looser converter.
But we do know the Demon ran well before. So that's good.
Tighter converter is definately less forgiving on the fueling and timing.
PRH
Well-Known Member
Soooooo..... what I’m hearing is there were no issues with how that carb worked...... with 3 hole emulsion and high position IFR.
PRH
Well-Known Member
I think you were right.......
That race Brawler “750” is looking pretty good about now.
Why did it get a tighter converter and taller tires?
Better on the street?
That race Brawler “750” is looking pretty good about now.
Why did it get a tighter converter and taller tires?
Better on the street?
I don't know if this valid to extrapolate from, but most of my headaches started after TurboAction tightened up the converter in my Barracuda (at my request).
Yes I messed with the carb (actually a several) but a big help was knocking some timing off (slowing the secondary advance) which starting a little lower in the rpm.
Its possible the the engine is seeing higher load (at those rpms), is spinning up just that much slower, and effecting the burn - or just making it less tolerant of too much lead (which the loose converter covered up like slipping the clutch so we don't stall an engine that isn't yet spinning at an rpm for load).
Yes I messed with the carb (actually a several) but a big help was knocking some timing off (slowing the secondary advance) which starting a little lower in the rpm.
Its possible the the engine is seeing higher load (at those rpms), is spinning up just that much slower, and effecting the burn - or just making it less tolerant of too much lead (which the loose converter covered up like slipping the clutch so we don't stall an engine that isn't yet spinning at an rpm for load).
I know i should just stop the bleeding and buy one. But a 100-200 dollar slips threw. 5-900 dollar purchase.
Put me in the dog house and questions why i'm spending that kind of money(I love my wife to death, but she don't get cars, and racing at all.)I'm and old man and my wife still think i will grow out of this silly thing.
If that 650 is old school tune, its pretty tempting to suggest racing that as test.
If it does the same thing, then the odds are good that the emulsion/MAB etc is not the primary culprit. You can come back and play with those things, but it may not be something that can be fixed with carburation alone (or injection for that matter).
If it does the same thing, then the odds are good that the emulsion/MAB etc is not the primary culprit. You can come back and play with those things, but it may not be something that can be fixed with carburation alone (or injection for that matter).
Hmm interesting thought, I have always heard that most carb stumble develop from NOT Enough initial time....... not to much. or am i miss understanding.
I'm 22 Initial and 38 total by 2800 rpm.
It's old school!
bought it well used in the late 90's was told it was a 750 and when i found out it was a 600 i threw it in the corner and forgot about it.
When i go frustrated with my vacuum secondary not giving me consistent enough ets, i pull the the 600 out. cut the chock tower off of it and lightly cleaned out the venuri as well as the seam in side the boosters. remove the standard butterfly screws for the round headed ones and ground on the throttle shafts for more airflow. This carb when on my 340 and ran for many a years.
When the 408 was built, it when on because it was a know good carb to break the motor in. Ran it for several years that way. Before the MITTY DEMON DARKEN MY HALLWAYS
I kept the initial about the same. But I slowed down the advance . First got the one distributor so about 26* at 2200, 32* at 3700 and 35 around 3200 rpm.
Then worked on another distributor with chrysler advance to get a better shape. But with either curve, the flat spot and pinging is gone. This is street and autocross. I did have the car at the 1/4 mile once while still working on the advances and the carb. It was a bit of dog off the line at least in part 'cause I had taken too much out early in the curve (about same initial). Early curve I mean 900 - 1600 rpm.
Converter is a 17505. Was 3000 rpm brake stall , probably about 2700 rpm now.
I assume your set up with a lot more power, a higher stall, and lower gearing even though taller tires.
My gut is to try slowing the advance so timing from 2800 might be 30 - 32 and 38* is above stall.
Be interested to hear what others think who have messed with tighter converters and more load (taller tires or less gear).
I'd give you two likes for that if I could.It's old school!
bought it well used in the late 90's was told it was a 750 and when i found out it was a 600 i threw it in the corner and forgot about it.
When i go frustrated with my vacuum secondary not giving me consistent enough ets, i pull the the 600 out. cut the chock tower off of it and lightly cleaned out the venuri as well as the seam in side the boosters. remove the standard butterfly screws for the round headed ones and ground on the throttle shafts for more airflow. This carb when on my 340 and ran for many a years.
When the 408 was built, it when on because it was a know good carb to break the motor in. Ran it for several years that way. Before the MITTY DEMON DARKEN MY HALLWAYS
So maybe its a 630 - 650 now with your mods!
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